This application claims Paris Convention priority of DE 101 51 961.3 filed Oct. 20, 2001 the complete disclosure of which is hereby incorporated by reference.
The invention concerns a device for processing (sharpening and polishing) a knife-edge comprising a slit which is provided in a base plate and is open to the outside, for guiding the knife-edge, and processing rods which are pivotably disposed in opposition to an elastically resilient restoring force on each side of the slit and which intersect in the region of the slit, wherein the knife-edge can be applied at their point of intersection.
In a known device of this type (U.S. Pat. No. 4,934,110), the restoring force for the processing rods is produced by a helical spring whose one end is mounted to the base plate and whose other end engages at the end of an arm of a two-armed lever whose other arm is rigidly mounted to a processing rod and is pivotably disposed about a bolt mounted in the base plate. In this known device, the axial deflection of the helical spring is relatively large when the point of intersection of the processing rods travels along the slit in the base plate from the outside to the inside. Consequently, the forces acting on the knife-edge at the point of intersection substantially depend on the spring characteristics and can therefore change over time in an undesirable manner. To obtain as flat a spring response as possible, a relatively long helical spring is required and therefore a large base plate. This makes the device cumbersome. Attempts have been made to keep the angle at which the processing rods abut the knife-edge during motion along the slit approximately constant through corresponding curvature of the processing rods. It has, however, not been possible to completely eliminate the influence of the spring characteristic response on the forces acting on the knife-edge at the point of intersection. U.S. Pat. No. 4,934,110 also discloses a device with which the restoring force acting on the processing rods is not generated by a spring, rather by weights. This device is heavy and can only be used in orientations in which the weights are moved by gravity.
It is the underlying purpose of the invention to develop a device which is as light and handy as possible with which the forces acting on the knife-edge remain as constant as possible during movement of the point of intersection.
This object is achieved in accordance with the invention in that each processing rod is rigidly connected at its pivot axis to the axis of an eccentric disc having a weight which is less than or equal to that of the processing rod(s) and on which a spring element, which produces a radial spring force on the eccentric disc, engages such that with the point of intersection being in the region of the outer end of the slit (original position) the spring element engages a location of the eccentric disc whose radial separation from the eccentric axis is smaller than the separation radius of the location where the spring element engages the eccentric disc when the point of intersection is in the region of the inner end of the slit.
Through the use of an eccentric disc in the load path between the pivot axis of the processing rods and the spring element, the deflection of the spring element can be as small as desired through selection of the eccentricity of the eccentric disc. This eccentricity must be sufficiently large that the spring element engaging on the eccentric disc produces a restoring force which pivots the processing rods back into their original position when the knife-edge is removed from the slit. The eccentric discs can be light discs, which, in and of themselves cannot reset the processing rods. The invention facilitates construction of a light and handy device, which the user can attach to his/her apron.
In embodiments of the invention, the spring element can engage the periphery of the eccentric disc or on an arc-shaped contact surface disposed inward of that periphery. In the latter case, this contact surface extending inward of the periphery of the eccentric disc can be the bottom of a groove, which is recessed in the periphery of an eccentric disc. In this embodiment of the invention, the sides of the groove prevent the spring element from sliding off the contact surface. This contact surface can also be provided as a rib on the eccentric disc, wherein the spring element is guided on one side. In embodiments of the invention, the eccentric disc can be shaped to form a shoulder in the region of the contact surface for the spring element such that this shoulder forms the contact surface and one side of the spring element is once more secured with respect to sliding off the contact surface by the side surface of the eccentric disc. This embodiment of the invention may be further developed in that a further disc is mounted to the side surface of the eccentric disc to guide the spring element on the side facing away from the eccentric disc.
In embodiments of the invention, the spring element can have different designs. In one embodiment of the invention, the periphery of a cylindrical helical spring, which is mounted at both ends to the base plate, abuts the eccentric disc tangentially, optionally under pressure. The helical spring is laterally deflected by the eccentricity of the eccentric disc against the spring force of the helical spring, with this deflection producing the restoring force which returns the processing rods into the original position when the knife-edge is removed from the device slit. The point of larger eccentricity of the eccentric disc can thereby slide along the periphery of the helical spring during lateral deflection of that spring. Use of a helical spring having tight, optimally pretensioned windings which abut each other is thereby advantageous.
In another embodiment of the invention, the spring element is a leaf spring whose one end can be rigidly connected to the base plate and with its free end cooperating with the eccentric disc to either seat on the periphery of the eccentric disc or on a surface recessed from that periphery.
In a further embodiment of the invention, a spring wire is used as spring element, which seats on the eccentric disc to constitute the above-mentioned helical spring.
In all of the above-mentioned embodiments of the spring element, the maximum spring element deflection is given by the degree of eccentricity of the eccentric disc during motion of the processing rods, and not by the degree of angular rotation and therefore not by the degree of pivoting motion of the processing rods. The overall device can therefore be relatively small.
The object of the invention can also be achieved by an inventive embodiment wherein each processing rod is rigidly connected at its pivot axis to a hub from the periphery of which an elastically resilient arm projects in a radial direction whose free end abuts a stop in the base plate. This arm acts like a leaf spring. When the point of intersection of the processing rods is in the vicinity of the inner end of the slit, this resilient arm is tensioned to a greater extent than in the original position of the processing rods and pivots the processing rods back into their original position when the knife-edge is removed from the slit.
This embodiment of the invention can be further developed in that the elastically resilient arm is integral with the hub and the arm and hub consist of plastic material forming a plastic injection-molded part, which is inexpensive to produce.
In embodiments of the invention, the spring element can be mounted to the base plate in a replaceable or removable fashion to facilitate cleaning of the device and of the spring element.
The device advantages of low weight and simplicity of production can be further improved by the following features.
The base plate can be produced as a molded component using plastic or light metal. Stops which are known per se can be injection-molded to the base plate for the pivoting motion of the processing rods. In embodiments of the invention, fastening means for the spring element can be injection-molded to the base plate to form e.g. bolts for mounting a helical spring or the like. The base plate can be inexpensively produced as an injection-molded part, also taking into consideration ergonomic points of view.
Finally, handling of the device is facilitated when the base plate has an opening, which can serve as a handle for accepting fingers of a hand. The pivot bearings for the processing rods (such as openings in the hubs, within which the processing rods are mounted) can already be provided in the base plate during injection-molding thereof.
Finally, the use of the inventive device is further facilitated when at least one recess is provided in the base plate for mounting the device to a base. In embodiments of the invention, this can be e.g. a recess (preferably a dovetailed recess) at the edge of the base plate with which the device can be pushed onto a corresponding holding part of a support.
The processing rods can be mounted to a hub passing through the base plate, an end of which bears the eccentric disc for secure mutual rotation therewith. This mounting can be realized in embodiments of the invention in that the hub has at least one radial opening through which an end of the processing rod can be guided. This ensures secure mutual rotation between the processing rod and, via the hub, the eccentric disc.
The processing rods can be connected to the hub in a replaceable fashion so that processing rods for polishing or sharpening the knife-edge can be connected to the hub, in dependence on the requirements. Processing rods can also be connected to the hub (acting as a pivoting bolt) which comprise a section for polishing the knife-edge and a section for sharpening the knife-edge (as is known per se).
Further features of the invention can be extracted from the following description of embodiments of the invention in connection with the claims and the drawing. The individual features can be realized in embodiments of the invention either individually or collectively in any arbitrary combination.
The drawing shows portions of two embodiments which are required for understanding of the invention.